The invention relates to a device for converting thermal energy into mechanical energy in a cycle process, wherein a gaseous working medium is pushed from a hot space through a heater, regenerator and cooler into a cold space and thereafter pushed back through the same passage into the hot space through the action of a piston.
One cycle process of this type is the well known Stirling cycle process, which is carried out in a cylinder equipped with a displacement piston and a working piston, wherein the cold space is located between the two pistons and the hot space is located between the displacement piston and the cylinder head. The volumes of the hot space and the cold space are periodically changed by a phase shifted hub movement of the two pistons. The output from this engine is picked up by the shaft which is connected to the two pistons through a rhombic drive.
Quite apart from the difficulties involved, especially in a single cylinder engine with a rhombic drive, it is also difficult to regulate r.p.m. and torque in an engine operating on the principle of the Stirling method. Optimized control by change in heat supply is too sluggish and therefore feasible in exceptional cases only. It has therefore been suggested to perform the control by changing the pressure level. This, however, requires an additional pressure pump and a pressure tank. Finally, one may also consider a bypass type control, which however must be regarded as a pure loss control, one which correspondingly reduces the efficiency. It is for these reasons that the Stirling method has not yet found widespread acceptance, in spite of its high thermodynamic efficiency and other advantages; for vehicle engines where fast load and r.p.m. changes are required, the suitability of the method is fundamentally questionable.